It is well established that mononuclear phagocytes are required for antigen recognition and lymphocyte activation, and that they play a vital role in the immune response of the host to infectious, inflammatory, and malignant disease. Several aspects of immunological function and host response to infection and injury are attributable to various proteins and other mediators released from stimulated mononuclear phagocytes (Dinarello, 1984). These include leukocytic pyrogen (LP), a mediator of fever; leukocytic endogenous mediator (LEM), an inducer of several components of the acute phase response; lymphocyte activating factor (LAF), which augments both lymphocyte proliferation and lymphokine production; and mononuclear cell factor (MCF), which induces prostaglandin E.sub.2 and collagenase synthesis in synovial cells. It has been demonstrated that LP and LAF activity co-purify and share common physical characteristics (Rosenwasser et al., 1979); Rosenwasser et al., 1981; Murphy et al., 1980). Similarly, there is evidence that LP and LEM are closely related, if not the same molecule (Kampschmidt, 1981), and furthermore that LAF and MCF seem to be identical (Mizel et al., 1979). The term interleukin-1 (IL-1) is now used to describe these varied biological activities, although it is presently unclear whether IL-1 represents a single substance or a family of related molecules. Prior to the subject invention, the art had no knowledge of the nucleotide sequence encoding human IL-1. Though the art was aware of general cloning procedures, there is no teaching or suggestion in the prior art which could be used to identify and clone the nucleotide sequence coding for human IL-1.